Make Mutex per-Fiber instead of per-Thread

* Enables Mutex to be used as synchronization between multiple Fibers
  of the same Thread.
* With a Fiber scheduler we can yield to another Fiber on contended
  Mutex#lock instead of blocking the entire thread.
* This also makes the behavior of Mutex consistent across CRuby, JRuby and TruffleRuby.
* [Feature #16792]

1 files changed, 12 insertions, 0 deletions

diff --git a/spec/ruby/core/mutex/owned_spec.rb b/spec/ruby/core/mutex/owned_spec.rb
index e66062534e..f881622965 100644
--- a/spec/ruby/core/mutex/owned_spec.rb
+++ b/spec/ruby/core/mutex/owned_spec.rb
@@ -40,4 +40,16 @@ describe "Mutex#owned?" do
       m.owned?.should be_false
     end
   end
+
+  ruby_version_is "2.8" do
+    it "is held per Fiber" do
+      m = Mutex.new
+      m.lock
+
+      Fiber.new do
+        m.locked?.should == true
+        m.owned?.should == false
+      end.resume
+    end
+  end
 end